You file it on schedule C in your personal 1040 tax return. You may need to send in quarterly estimated payments to cover the self employment tax on it since there is no withholding taken out. Oh, is it a Single Member LLC? Did you elect to be an S corp? If you are an S corp you need to file a separate 1120 S business return for it.
FOR SCHEDULE C SELF EMPLOYMENT:
To report your self employment income you will fill out schedule C in your personal 1040 tax return and pay SE self employment Tax. You can enter Self Employment Income into Online Deluxe or Premier but if you have any expenses you will have to upgrade to the Self Employed version. Or any of the Desktop programs. But you will get the most help in the Home & Business version.
Turbo Tax Self Employment info
https://turbotax.intuit.com/tax-tips/self-employment-taxes/beginners-tax-guide-for-the-self-employed/L2HLojrj5
How to enter income from Self Employment
https://ttlc.intuit.com/community/self-employed/help/how-do-i-report-income-from-self-employment/00/26653
You might want to use Quicken or QuickBooks to keep tract of your income and expenses. There is one called QBSE QuickBooks Self Employed that works with Online Turbo Tax and will give you a free online tax return next year.
https://quickbooks.intuit.com/self-employed
You need to report all your income even if you don't get a 1099NEC or 1099Misc. You use your own records. You are considered self employed and have to fill out a schedule C for business income. You use your own name, address and ssn or business name and EIN if you have one. You should say you use the Cash Accounting Method and all income is At Risk.
After it asks if you received any 1099NEC it will ask if you had any income not reported on a 1099NEC. You should be keeping your own records. Just go through the interview and answer the questions. Then you will enter your expenses.
Self Employment tax (Scheduled SE) is automatically generated if a person has $400 or more of net profit from self-employment. You pay 15.3% SE tax on 92.35% of your Net Profit greater than $400. The 15.3% self employed SE Tax is to pay both the employer part and employee part of Social Security and Medicare. So you get social security credit for it when you retire. You do get to take off the 50% ER portion of the SE tax as an adjustment on 1040. The SE tax is already included in your tax due or reduced your refund. The SE tax is in addition to your regular income tax on the net profit.
Here is some IRS reading material……
IRS information on Self Employment
https://www.irs.gov/businesses/small-businesses-self-employed/self-employed-individuals-tax-center
1040 Schedule C Instructions
https://www.irs.gov/pub/irs-pdf/i1040sc.pdf
Publication 535 Business Expenses
https://www.irs.gov/pub/irs-pdf/p535.pdf
Your income taxes will be filed annually on Schedule C which is included as part of your personal tax return. You may need to make quarterly estimated tax payments to cover your income tax and self-employment tax for your sole proprietorship. The information provided by Champ VolvoGirl explains more about the self-employment tax. Whether or not you owe any self-employment tax or additional income tax for your Schedule C depends on whether you have an overall gain or loss from your sole proprietorship. If you have a loss for the year, then no quarterly payments would have been required.
The quarterly payments may be required because the IRS considers the tax system to be a 'pay as you go' system. You can certainly reconcile everything one time per year when you complete your tax returns, but there could be penalties for not making estimated payments throughout the year.
Since you also have a W-2 job where taxes are being withheld throughout the year, you can consider increasing those withholdings in order to cover the taxes for your Schedule C instead of making quarterly payments. As long as the taxes are paid throughout the year and not just when you file your return you can avoid any additional penalties.